[Q] Change WCDMA frequencies to 850Mhz topic

I currently live in Argentina, and I bought this Galaxy Core Duos from the USA.

When I first tried, I noticed that just GSM/2G network was working, and after doing some research, I found out that I have to change the WCDMA/3G frequencies to 850Mhz.

I've seen on the Internet that you gotta dial *#197328640# and follow some steps, but I'm not able to get into that "service menu"...

Please feel free to ask for some information if needed.

Cheers